You are a producer for a rolling news channel, under pressure to deliver a guest to discuss one of the day's big talking points. The major players in the story either have their phones switched off, or they are busy, or they refuse to take part. But the clock is ticking and you have a four-minute slot to fill. And the realistic chances are that if you cannot find anyone else, you end up booking someone from a lobby group.

If the subject is crime, producers will often turn to Norman Brennan from the Victims of Crime Trust; if it is immigration, try Sir Andrew Green from MigrationWatch; for life, birth or death, your woman is Josephine Quintavalle from Comment on Reproductive Ethics (Core). Sometimes they are booked because of an intervention their organisation has made - a survey, speech or piece of research. But often, their ubiquity is down to the fact that they keep their mobiles turned on and they can make it down to the Millbank TV studios for a 7.35am slot.

Axes to grind

The consequence over time is that, by using them so often, news channels create a profile for a hard core of spokesmen and women which often transcends their actual importance. Their repeated exposure conveys on these commentators a sense of authority that viewers may come to accept. They are transformed into establishment figures, taken for granted as representatives of a public consensus and genuine stakeholders in a debate, even though they may not represent anyone other than themselves, or a handful of members with personal axes to grind. They are placed on a par with elected politicians and accountable public figures.

Last month, on the afternoon the government lost the 90-day terror suspect detention vote, I was working for the London radio station LBC 97.3 at Millbank. I was struck by what was happening on College Green, where a phalanx of camera crews were waiting. Every channel was on open-ended coverage, and the producers needed guests. But the politicians, those who had made the decision, remained in the warmth of the Commons lobby. Some were indeed being interviewed from there, but the crews on the green needed to show they were doing something.

Fortunately, on hand were Shami Chakrabarti, director of Liberty, and Sir Iqbal Sacranie from the Muslim Council of Britain. Both are well-informed and articulate, but neither has a democratic mandate to make our laws, nor had taken part in the vote. Yet by interviewing them in the same context as politicians the implication was that they were playing an equally weighty role in the unfolding events.

Everywhere on TV and radio, debates are being framed by lobby-group spokespeople whose credentials and authority to speak are not always clear. Groups like People for the Ethical Treatment of Animals; Hacan ClearSkies (the anti-Heathrow expansion campaigners), Fathers 4 Justice, Kevin Miles from the Football Supporters' Federation, Mediawatch, the Portman Group and Christian Voice.

But who are these people? Who decided they deserved a self-appointed role in proceedings equal to the professionals? Who scrutinises them? And do they represent the mass of public opinion, or just a narrow self-serving interest group? Do they appear on TV and radio for the value they provide, or just because they are available for an interview? In a busy newsroom and with airtime to fill, it is sometimes difficult to resist the temptation to go for an "easy hit" or, as they are sometimes known, "a low-hanging fruit". I have been guilty of it myself.

Mystical qualities

Josephine Quintavalle of Core puts her popularity down to the unique nature of her role. "I get a high profile because I focus on a very specific area. I'm not on an ego trip - I wish there were more people getting their heads around reproductive ethics." But she admits: "We are based in London, so it's easier to get to Millbank - that's why we're booked." Core is not a membership organisation but a loose network of similarly minded people, so who does she represent? "A broad but conservative section of society - what I say is credible because it's the truth."

There is often no relationship between the group's size and the extent of its exposure. Norman Brennan of the Victims of Crime Trust, which comprises just a few people, has racked up over 7,000 broadcast interviews since 1994. Sir Andrew Green, of MigrationWatch UK, a thinktank with no formal membership, has been interviewed 400 times in the past three years. But, he argues, research endorses his claim to be putting popularly-held concerns on the news agenda. "Viewers can see someone making an argument they agree with, but are afraid to voice themselves. Our view represents 70% of the public who support, according to opinion polls, tighter restrictions on immigration."

Nick Pollard, head of Sky News, says such figures have an important role in airing widely held views that would not otherwise have been heard. "There's a great deal of support for [Brennan's] view in the wider public but it doesn't tend to have a voice. The pro-welfare for asylum seekers lobby is very vocal, but there is not much of a vocal lobby from the other side. These people do serve a purpose. I don't think we imbue them with any great mystical qualities but they articulate an opinion shared by a lot of people." He also cites the credible research which underpins the authority of some of them: "There's a lot of documentation that the government takes [Green's] views seriously, and there have been occasions when the MigrationWatch figures have been more reliable than the official ones."

Guts of an argument

Peter Horrocks, head of BBC TV news, denies broadcasters are responsible for turning talking heads into figureheads. "Many organisations had respectability and authority before the advent of 24-hour news. They represent a single clear point of view, and often know more about it than politicians, especially backbenchers. And they can explore the guts of an argument more clearly than a politician."

Are audiences allowed, though, to misinterpret a spokesperson's role in a story? Horrocks does not believe that the likes of Shami Chakrabarti is ever put on the same footing as Charles Clarke. "The key is not to take them at face value. We might explain that their research has a particular bent." But, Pollard says, there is only so much you can do to contextualise any such guest. "We have between 60 to 100 interviews a day, and it's not realistic to go into the background of each one. But we try to indicate where they're coming from, and if they have an axe to grind, what that axe is."

On a screen near you

Norman BrennanVictims of Crime Trust

Brennan is the founder of this group, which has two staff and no members Broadcast interviews: 7,000 since 1994

Josephine QuintavalleComment on Reproductive Ethics (Core)

Takes a broadly conservative stance on reproductive issues, has a contact base of 1,500 but no members Broadcast interviews: "Several hundred" since 1994

Andrew GreenMigrationWatch UK

Green claims to have "brought public opinion into focus ... on the scale of migration" with his thinktank, which has no formal membership Broadcast interviews: 400 since 2002

Shami ChakrabartiLiberty

Chakrabarti is the director of this 8,000-member pressure group, which has an elected council. "Twenty-four hour news channels provide a useful forum for key issues that might otherwise get left behind," it says Broadcast interviews: about 10 a week

John BeyerMediawatch UK

Beyer is the elected director of the successor organisation to Mary Whitehouse's National Viewers' and Listeners' Association, with a membership of 5,000 Broadcast interviews: 1,000 since 1994